In a recent year, organic light-emitting diodes, due to advantages such as self illumination, fast response speed and low power consumption, have been widely used in display and illumination applications. Generally, the organic light-emitting diode can be categorized to a top-emitting type, a bottom-emitting type and a two side-emitting type.
Please refer to FIG. 1, which is a schematic cross-sectional structure view of a bottom-emitting-type organic light-emitting diode in accordance with prior art. As shown, the bottom-emitting-type organic light-emitting diode 100 includes a metal layer 10, an organic light-emitting layer 12, a transparent conductive layer 14 and a transparent substrate 16.
When the organic light-emitting diode 100 is supplied with a specific voltage, electrons (not shown) and electron-holes (not shown) are combined to each other and emit lights with various emission angles (for example, lights 121, 123 and 125). Because the organic light-emitting layer 12 has an optical refraction smaller than that of the transparent conductive layer 14, the lights 121, 123 and 125 each can successfully emit into the transparent conductive layer 14 from the organic light-emitting layer 12.
Then, because the organic light-emitting layer 14 has an optical refraction greater than that of the transparent substrate 16, the light 121 with a relatively large emission angle in the transparent conductive layer 14 is totally reflected back to the transparent conductive layer 14 or even the organic light-emitting layer 12 from a surface between the transparent conductive layer 14 and the transparent substrate 16, and hardly emits to the air 18. Base on the same manner, because the organic light-emitting layer 14 has an optical refraction greater than that of the air 18, the light 123 with a relatively large emission angle in the transparent substrate 16 is totally reflected back to the transparent substrate 16 or even the transparent conductive layer 14 from a surface between the transparent substrate 16 and the air 18. Accordingly, only the light 125 with a relatively small emission angle can emit into the air 18 sequentially through the organic light-emitting layer 12, the transparent conductive layer 14 and the transparent substrate 16. Thus, the light coupling efficiency from the inner to the outer (or, the air 18) of the organic light-emitting diode 100 is only about 15% to 20%, if without any optical compensate design.
Today, in some optical compensate designs, an optical diffusion film is disposed at one side of the organic light-emitting diode 100 (specifically, the bottom surface of the transparent substrate 16) so as to enhance the light extraction efficiency of the organic light-emitting diode 100.